This invention relates to heat pumps and particularly to heat pumps suitable for northern climates which are subjected to a wide range of ambient temperatures.
Heat pumps are known which provide both heating and cooling. Heat pumps to be used in northern climates encounter special problems that have required additional complexity of construction to overcome. One of the main difficulties is that northern climates require high heating capacities and less cooling capacities while conventional heat pumps have nearly equal cooling and heating capacities. One prior approach to reducing the cooling capacity while maintaining high capacity in the heating mode involves the use of two compressor motors or a motor adapted to operate at a slower speed in the cooling mode. Another approach that has been prepared is to use a restrictor in conjunction with check valves that restricts flow in the cooling mode. These approaches add complexity and cost to the system and do not provide a desirable degree of adjustment of capacity for all temperature conditions with the result that the desired on-off cycling times and humidity control is not achieved.
Another inherent problem with heat pump occurs when the four-way reversing valve is switched, such as for defrosting the evaporator, or for changing from the heating mode to the cooling mode, or vice versa. At the moment the system is reversed, the compressor inlet pressure is higher than the outlet pressure which has two adverse effects on the system. One is that the reversed pressure causes the compressor to drive the electric motor momentarily which has undesirable electrical effects. The other is the danger of liquid refrigerant entering the compressor which can damage the compressor. The conventional method of dealing with this latter problem is the use of a suction line accumulator to trap the liquid.